1. Field of the Invention
The present invention relates to a fuel cell system including a fuel cell formed by sandwiching an electrolyte electrode assembly between a pair of separators. The electrolyte electrode assembly includes an anode, a cathode, and an electrolyte interposed between the anode and the cathode.
2. Description of the Related Art
Typically, a solid oxide fuel cell (SOFC) employs an electrolyte of ion-conductive solid oxide such as stabilized zirconia. The electrolyte is interposed between an anode and a cathode to form an electrolyte electrode assembly (unit cell). The electrolyte electrode assembly is interposed between separators (bipolar plates). In use, a predetermined numbers of the unit cells and the separators are stacked together to form a fuel cell stack.
In the fuel cell, an oxygen-containing gas or air is supplied to the cathode. The oxygen in the oxygen-containing gas is ionized at the interface between the cathode and the electrolyte, and the oxygen ions (O2−) move toward the anode through the electrolyte. A fuel gas such as a hydrogen-containing gas or CO is supplied to the anode. Oxygen ions react with the hydrogen in the hydrogen-containing gas to produce water or react with CO to produce CO2. Electrons released in the reaction flow through an external circuit to the cathode, creating a DC electric energy.
As an example of the fuel cell stack formed by stacking a plurality of fuel cells, a fuel cell stack disclosed in Japanese Patent No. 3,251,919 is known. According to the disclosure of Japanese Patent No. 3,251,919, as shown in FIG. 9, a fuel cell stack 2 is disposed in a pressure casing 1, and the fuel cell stack 2 is surrounded by thermal insulation material 3. Upper and lower tightening plates 4a, 4b of the fuel cell stack 2 are tightened by cylindrical tightening bolts 5.
Current terminals 6a, 6b are provided at upper and lower positions of the fuel cell stack 2. The current terminal 6a is connected to a current cable 7. The current cable 7 is inserted into one of the cylindrical tightening bolts 5, and connected to a current outlet 8a. The current terminal 6b is connected to a current outlet 8b adjacent to the current outlet 8a. A purge gas inlet pipe 9 is connected to the tightening bolts 5. A purge gas for cooling the current cable 7 is supplied through the purge gas inlet pipe 9.
Typically, fluid units such as a heat exchanger for heating an oxygen-containing gas and a reformer for reforming a fuel gas are provided for the fuel cell stack 2. However, in the structure of Japanese Patent No. 3,251,919, the fluid units cannot be suitably disposed in the pressure casing 1.
Further, the current cable 7 is inserted into the cylindrical tightening bolt 5, and the purge gas inlet pipe 9 for supplying the purge gas which cools the current cable 7 is connected to the tightening bolts 5. Therefore, the structure of the fuel cell stack 2 is complicated, and the production cost of the fuel cell 2 is high. Further, the layout of the fluid units is difficult.